Analysis of bHLH genes from foxtail millet (Setaria italica) and their potential relevance to drought stress

Foxtail millet is very a drought-tolerant crop. Basic helix–loop–helix (bHLH) transcription factors are involved in many drought-stress responses, but foxtail millet bHLH genes have been scarcely examined. We identified 149 foxtail millet bHLH genes in a genome-wide analysis and performed Swiss-Prot, GO, and KEGG pathway analyses for these genes. Phylogenetic analyses placed the genes into 25 clades, with some remaining orphans. We identified homologs based on gene trees and Swiss-Prot annotation. We also inferred that some homologs underwent positive selection in foxtail millet ancestors, and selected motifs differed among homologs. Expression of eight foxtail millet bHLH genes varied with drought stress. One of these genes was localized to a QTL that contributes to drought tolerance in foxtail millet. We also perform a cis-acting regulatory element analysis on foxtail millet bHLH genes and some drought-induced genes. Foxtail millet bHLH genes were inferred to have a possible key role in drought tolerance. This study clarifies both the function of foxtail millet bHLH genes and drought tolerance in foxtail millet.